How to practice Fermi estimation
Try to say your assumptions out loud—or write them down—before submitting a number. A useful estimate is transparent enough that another person can follow the path from assumptions to answer.
- Identify the population, area, time period, or other base quantity.
- Estimate the rate or fraction that connects it to the question.
- Multiply, divide, and check whether the result is plausible.
Question examples
Each example below has a reference answer and a reasoning path. Open one to make a standalone estimate before reading the explanation.
- U.S. gasoline consumption per day (2025)Everyday
- U.S. eggs produced per day (2025)Everyday
- Distance from Earth to the SunScience
- Global lightning flashes per dayScience
- New York City population (2025)Geography
- Worldwide airline passenger journeys (2025)Geography
- Functioning satellites in Earth orbit (July 2026)Technology
- Global data-center electricity use (2025)Technology
- People using the Internet worldwide (2025)Technology
- Walmart associates worldwide (2026)Business
- Starbucks stores worldwide (Q3 FY2026)Business
- Amazon same/next-day Prime items per day (2025)Business